From an Easily Accessible Pentacarbonylcobalt(I) Salt to Piano‐Stool Cations [(arene)Co(CO)₂]⁺

Abstract

The facile synthesis of a pentacarbonyl cobalt(I) salt without the need for a superacid as solvent is presented. This salt, [Co(CO) ] [Al(OR ) ] {R =C(CF ) }, readily accessible on a multigram scale, undergoes substitution reactions with arenes yielding the hitherto unknown class of two-legged cobalt piano-stool complexes [(arene)Co(CO) ] with four different arene ligands. Such a substitution chemistry would have been impossible in superacid solution, as the arenes used would have been oxidized and/or protonated. Thus, the general approach described herein may have a wide synthetic use. Additionally, the thermochemistry of the piano-stool complexes is shown to be not easy to describe computationally and most of the established DFT methods overestimate the reaction energies. Only CCSD(T) calculations close to the basis set limit gave energies fully agreeing with the experiment.

How does the Environment Influence a Given Cation? A Systematic Investigation of [Co(CO)5]+ in Gas Phase, Solution, and Solid State

“…Thus, it appeared interesting to analyze the subtle influence of the environment (gas phase, condensed phase) on a larger series of [Co(CO) 5 ] + [WCA] − salts with respect to the structural deformations of [Co(CO) 5 ] + and its consequences on the ν(CO) bands. This builds upon our earlier report of [Co(CO) 5 ] + [Al(OR F ) 4 ] − , and by using the same synthetic methodology, a series of five [Co(CO) 5 ] + salts or modifications with anions ranging from almost non‐interacting (viz. [F{Al(OR F ) 3 } 2 ] − ) to clearly interacting (viz.…”

“…The compound initially assigned as [Co(CO) 4 ] + (solv) in HSO 3 F or HSO 3 F/SbF 5 solution was later assumed to be [Co(CO) 5 ] + , for which δ 13 CO values between 182.1 and 186.1 ppm were reported . The 13 C NMR spectrum of 2 in o ‐DFB solution contains one broad signal at 181.6 ppm, which indicates active Berry pseudorotation that equilibrates the axial and equatorial signals of [Co(CO) 5 ] + . Similarly, the δ 13 CO signal of 3 is observed at 181.4 ppm.…”

“…As a reference for later discussions, we performed calculations based on the (RI‐)B3LYP‐D3/def2‐TZVPP level of theory for the TBP and SP structures of [Co(CO) 5 ] + . This level of theory emerged from others, as well as own work, as being very reliable for this system . As is typical for a transition state structure, the vibrational analysis gave rise to an imaginary frequency ( i 45 cm −1 ) for the SP.…”

“…The compounds [Co(CO) 5 ] + [F{Al(OR F ) 3 } 2 ] − ( 3 ) and [Co(CO) 5 ] + [F‐Al(OR F ) 3 ] − ( 4 ) were prepared in o ‐DFB solution under 2–3.5 bar CO pressure for >1.5 h at room temperature [Eq. ] by the procedure described recently for [Co(CO) 5 ] + [Al(OR F ) 4 ] − ( 2 ). …”

N‐Heterocyclic Carbene Stabilized Dicarbondiphosphides: Strong Neutral Four‐Membered Heterocyclic 6π‐Electron Donors

“…It is not surprising that in the cationic cobalt complexes [Co(CO)(η 4 ‐L 2 C 2 P 2 )] + 5 a , b and 6 a , b the ν(CO) increases to values in between 1942 to 1998 cm −1 . But these stretching frequencies are still much lower in energy than the ones observed in the benzene complex [Co(CO) 2 (η 6 ‐C 6 H 6 )] + [ν(CO)=2113, 2078] or even the neutral cyclopentadienide complex [Co(CO) 2 (η 5 ‐C 5 H 5 )] [ν(CO)=2026, 1961] (see bottom of Table ). Within each series of complexes the ones with the unsaturated NHC substituent IPr (labelled a ) show slightly lower ν(CO) wave numbers than those with an SIPr substituent (labelled b ), and is consistent with the better electron‐donating properties of IPr compared to SIPr .…”